1. Field of the Invention
The present invention relates to a printer and a printing method using a plurality of print heads for sequentially recording a plurality of frames on a continuous recording material.
2. Background Arts
There are various types of color printers, e.g. ink jet printers, thermal wax transfer printers, thermal dye sublimation printers, and direct color thermal printers. The ink jet printer records color images by ejecting ink on a recording material by a print head. The thermal wax transfer printer and the thermal dye sublimation printer overlay an ink ribbon on the recording material and transfer the ink to the recording material by heating the ink ribbon by a thermal head (a print head). The direct color thermal printer performs recording by heating color thermosensitive recording paper formed of overlaid thermosensitive coloring layers, each of which develops different color, by the thermal head.
There are a multi-pass one-head type color printer and a one-pass multi-head type color printer. The one-pass multi-head type color printer has an advantage in that a shorter time is required for recording the color images. In the one-pass multi-head type color printer, a plurality of print heads are disposed along a feeding passage of the recording material, and each print head records the recording material in a different color to print the color image while feeding the recording material. The one-pass multi-head type color printer uses a continuous recording material and sequentially records a plurality of images along a lengthwise direction of the recording material. A blank area, which corresponds to an interval between a feed roller pair and the thermal head, is created between the areas (referred to as recording areas) in which the images are recorded. The blank area is a non-image area which is cut away from the recording area and discarded upon completion of the recording. The blank area may be left unprinted, or may have the images which protrude from the recording area in front of or behind it.
The print head of the color printer consumes a large amount of power. Therefore, there is a significant difference in the amount of power consumption of the one-pass multi-head type color printer between when one print head is operated and when a plurality of print heads are concurrently operated. As a result, a load in the power source circuit of the color printer fluctuates by a large amount. When the load in the power source circuit fluctuates, output voltage and output current amount also fluctuates. Such fluctuations change driving condition of the print head, so that recording density of the print head is varied.
When the recording density varies, unexpected density variation appears in a color print, which reduces image quality. In order to prevent the reduction of printed image quality caused by the load fluctuations in the power source circuit, a color printer disclosed in, for instance, U.S. Pat. No. 5,847,742 (See FIG. 13) regulates each interval Lh1 between the print heads 70-72 to be a length Lp1 which is a sum of the length W1 of each recording area 74a-74c and the length W2 of a blank area 75 of the recording material 73. Thereby, the print heads 70-72 concurrently perform recording in the recording areas 74a-74c and concurrently face a blank area 75.
However, since there are a plurality of print heads, when the interval Lh1 between the print heads are set to be the sum of lengths of the recording area W1 and the blank area W2, the color printer becomes upsized, and a feeding distance of the recording material is extended. Consequently, there arises a problem that the printing speed is reduced.
Further, in cases where length of the recording area is changed, or printing is performed in a plurality of the recording areas with different lengths in one sequence, at least one of the plural print heads inevitably faces the blank area between the recording areas while the remaining print heads face the recording areas. Conventional color printers stop the printing operation of the print head which faces the blank area. Therefore, the recording density varies according to the load fluctuations in the power source circuit. Such problems can be solved by using a power source circuit which is not affected by a change in the number of print heads in operation. However, another problem arises in that such power source circuit increases manufacturing costs of the color printer.